The invention relates to a built-up multiple cam, a camshaft having at least one built-up multiple cam and to a method of producing a camshaft having at least one built-up multiple cam.
The further development in the field of valve-controlled internal combustion engines places ever greater demands upon the camshafts utilised for controlling the valves. An important trend resides in the use of techniques for the variable control of the valve control times. Most recently, systems have become established, in which the valve lift is controlled by two mutually different cam contours, so that it is possible to switch between two different valve lifts. For this purpose, camshafts are used having multiple cams, on which at least two different cam contours are formed. The “VarioCam Plus” system which is utilised in vehicles produced by the company Porsche can be described as an example of this type of system. In the case of this system, so-called switchable bucket tappets are used, the mode of operation of which is known to the person skilled in the relevant technical field.
In order to improve the manner in which the forces are distributed in the force flow between the cam and the cam follower (e.g. a switchable bucket tappet), the cam is typically divided into three parts, wherein between two identical, axially mutually spaced apart outer cams having an identical cam contour there is disposed an inner second cam having a second cam contour which is different from the cam contour of the outer cams. It is known from the prior art that multiple cams of this type can be formed e.g. by milling in one piece or by grouping together three separate cams.
DE 196 06 732 C2 discloses multiple cams which consist of several individual parts which are assembled in the axial direction. The individual parts are formed by tube portions, of which portions are non-circular and which comprise concentric annular projections on the mutually facing ends. These projections are assembled together in order to form a multiple cam from the individual parts. These concentric annular projections are formed having a circular cross-section and are approximately half the wall thickness of the tube portion. This ensures that after the individual parts have been assembled together the complete wall thickness of the tube portions is provided even in the region of the assembled projections.
The multiple cams which are known from DE 196 06 732 C2 have the disadvantage that the connection between the individual parts is comparatively weak in the region of the concentric annular portions. In particular, the connection between the individual parts is not sufficiently torsion-resistant. In addition, the multiple cams which are disclosed in DE 196 06 732 C2 are only suitable for those camshafts which are produced according to the process of hydroforming.